The Duke of Cambridge marked becoming royal patron of a homeless charity by serving lunch to its clients – and quipped he was on trial for a job.

Wearing an apron, William dished out spaghetti bolognese to men and women who had patiently queued for the free lunch made by staff and volunteers.

The duke has become the figurehead of The Passage, an organisation which has helped more than 130,000 people in crisis over almost 40 years through its resource centre, homelessness prevention projects and innovative accommodation services.

William’s mother Diana, Princess of Wales first took him and younger brother Harry to the charity in December 1993, and as a young man the duke has made numerous public and private trips to the organisation.

Helping to chop carrots for lunch, the duke joked: “I feel Mary Berry is going to pop out in a minute and tell us we’re too slow.”

Mick Clarke, chief executive of The Passage, later joined William as he ladled the meat sauce on to pasta and joked to a client: “We’re giving him a trial.”

The duke, who was visiting the charity’s St Vincent’s Centre in Westminster, laughed and replied: “Yes, see how I get on.”

First in the queue for lunch was Taffy, who had been sleeping rough for almost 25 years before getting permanent accommodation five years ago, but he still returns to The Passage for some meals.

He said he had joked with William about his title: “I said to him ‘you’re the duke of Cambridge?’ and he said ‘yes’, and I said ‘I’m from Cambridge, I was born in Cambridge’.”

The 60-year-old was not fazed by being served by the duke, saying: “It doesn’t mean nothing, I just wanted to meet him. He’s just another geezer to me.”

Lunch is prepared for around 150 people a day but the charity has reported a significant rise during the past 12 months in the number of rough sleepers visiting its St Vincent’s Centre, with numbers increasing by almost 50% to more than 3,200.

When William joined the volunteers and staff preparing lunch, he first washed his hands and then made his way to a work surface with a chopping board and large box carrots.

He was then shown a quick way to peel and chop up the vegetables by the charity’s chef Nour Dakoba.

When Mr Clarke told the duke that a volunteer was thinking about bringing out a cookbook to mark its 40th anniversary next year, the royal quipped: “You don’t want any of my recipes, that’s for sure, they’re not worth being written in a book.

“And they’re not very healthy either, a few burgers and pizzas.”

The conversation later became more serious and the duke told volunteer Kyle Simon: “I’ve been thinking recently about all the cold weather, I always worry when I hear there’s snow forecast.”

William last visited St Vincent’s with wife Kate in the run-up to Christmas, when he spoke out against the drug spice after hearing about its devastating effect on the capital’s homeless.

He brought up the subject again on Wednesday when he told how he had come across users while a pilot with the East Anglian Air Ambulance.

He said: “We went to a few people who had taken spice with the air ambulance, and that whole process was very challenging, very sad seeing the destruction it has had on people’s lives.”

William ended his tour by meeting participants in the charity’s Home for Good project, a befriending scheme where trained volunteers are matched with a former homeless person becoming independent and living in their own accommodation.

After hearing one man’s successful battle against addiction and how he is forging a new life with support from his charity partner, William mentioned his work as patron of Centrepoint, a charity that tackles youth homelessness, but said young people face different issues like relationship problems.

He added: “Coming here really does open my mind to how the older you are, the more likely addiction is going to get hold of you, and how difficult it is to tackle.”